Process of making porous siliceous objects



.dust have failed. Thus Patented Aug. 17, 1926.

UNITED STATES PATENT- OFFICE.

rammed xnnn AND rnnnnarcx 1:. man, or summons, MARYLAND.

rnocnss or mine ron'ous smrcnous omc'rs.

1T0 Drawing-.

Our invention rel'atesto the art of making porous brick and other porousbodies of clay and similar plastic materials.

It has been proposed heretofore to make porous brick by mixing. withclay from 20 to 40 per cent by weight of sawdust, depending upon theplasticity and binding quality of the clay; adding water to the mixtureto forms, paste; forming bricks or other desired shapes; and then dryingand burning the bricks or other objects. -During the burning. operation,the Sawdust in the plastic mass is consumed, leaving pores or cells' inthe finishediproduct, the number of such cells corresponding to thenumber of particles contained in'theoriginal plastic mixture. Theproducts obtained by the method referredto have been found to be insuf-A to absorb most of the added water, thus militating against thenecessary function of the water in binding the materials together dursing the drying stage. The disadvantageous effect is further magnifiedby excessive Again,

' cernsthe behavior of the sawdust, but it has simultaneously clay '45swelling .ofthe. sawdust, and when this swelling takes placeafter thebricks or other shapes have been formed, cracks mayv ven before thedrying stage begins. when the bricks are heatedan enormous quantity ofwater is vaporized, and this vapor, breaking through the clay, tends tostrain the structure of the bricks while, the binding strength of theparticles is being weakened ijby the shrinking of the sawdust, thuscausing ad ditional fissures and partings in the dried develop shapes.Efforts to'control the absorptive.

and expansive qualities of sawdust by imregnating it with moisturerepelling agents have been partially successful, so far as conbeen foundI that the moisture repelling agents thus far employed have.deleteriously affected the chemical and physical properties of thesilicates. The obj ect of our invention 15130 eliminate 'quence, to-

parts of water, the binding- Application filed. December 14. 1925.Serial xo. '75.aas.

the difiiculties outlined above and, in conseroduce brick and otherobjects formed of ied and burned clay or the like having higher combinedporosit an strength than have heretofore been 0 tained in such products;With this object in view, our invention contem lates, in part, thesubstitution for the cru e sawdust or impregnated sawdust of the priorart, of a material 'which has superior attributes for the purpose.

We have found: that partial volatilization of wood, at relatively lowtemperatures, yields a product which in a very marked de-' gree lacksthecapacity for. taking up water and swelling, whlch rendei's the use ofcrude sawdust so. objectionable, as explained above. Moreover, thisproduct has low resiliency and elasticity, as compared with crudesawdust, so that the former, unlike the latter, may be; closelycompacted when mixed with clay and subjected 'topressuie.

If wood, in the form of'lumps, chips or dust, isheated, under exclusionof air, at a relatively low temperature, water vapor and small amountsof 'li ht volatile 'suba stances such as acetic ai carbon monoxide anddrawn ofi'. Partial vaporization of the nature referred to dissociatescellulose and dioxide and hydrocarbons, will be I breaks down more orless of the-cell strucv ture. A given quantity of raw sawdust, treatedin the above described manner, yields a quantity of modified woodsubstance which is from 10m 40% less by weight.

Though the substance thus obtained has e same-absorptive. ualities asrawv abo V v ablyswell upon abs bing water 'n'or' The following specific"formula will give good results:

Feed raw into a'clos'ed or partially closedheating receptacle andsubject it to a temperature of about 325 C. forabout 10 minutes? Aconvenient device for. this purpose is a cast iron act when -dr1'ed..

wood in broken or dust f brin or steel container provided with inlet anddischarge ports and having a feedingdevice j adjusted to progress thewood through the container-and discharge it after 10 minutes of heating.After the heat treatment permit the wood to cool and reduce it, ifrequired, to a finely divided state. Then mix .125 pounds of thisspecially prepared wood substance with 100 pounds of refractory clay,add water to form a paste, form the stage at relatively the mineralcomponents of the clay act as catalysts and volatilization takes placeat a lower temperature (200 C.) than in the first example (325? (1.).

As indicated by the examples given,the partial volatilization of thewood may take place at any time before the mixture is formed into shapesand subjected to pres sure and burning. It should be understood alsothat, while two substantially definite temperatures have been given aspreferable under the conditions recited in the illustrative examples,nevertheless the benefits of our invention may be realized in varyingdegrees by employing temperatures other than those mentioned andcontinuing the heat treatment for longer or shorter periods than thosestated. However, it is desirable on the one hand, to carry thevolatilization to a point where the modified wood product will have thedesired attributes in a substantial degree, and on the other hand, thevolatilization should stop considerably short of complete carbonization.It is preferable to leave in the roasted wood large quantities ofpyrolignic acid, besides acetic acid, ace tone and light tar. Thesecomponents will be readily consumed during the burning low temperatures,thus causin the formation of numerous cells in the brlck even beforethemaximum temperature has been reached inthe kiln. 'A completecarbonization of the wood in the preliminary treatment is undesirable,among other reasons, because exothermically in the kiln, would generatean excessive amount of heat and tend to produce a fused dense mass,

the preliminary heating of the wood should be conducted under conditionswhich will or by excludin .make the action exclusively endothermic.

This condition may be maintained by keeping the vaporizlng temperaturebelow the ignition point of the combustible substances air during thepreliminary heating, or hot expedients may be used.

The best modified wood product fOIk the purposes Stated'is one whichvolatilizaf 'tion'has been carried to vthe point at which the producthas a ark brown color. At. this stage therewil have be'en' little or novaporization of acetone, the cellulose will be dissociated but not thelignine." The volatile combustibles (acetones, light tars etc.) which ofwoody substance,

charcoal, burning In general,

are left in the modified wood substance have an important functionduring the burning stage, for we find that the whole mass including allof the carbon, will be consumed at a temperature considerably lower thanthe temperature necessary to completely consume an equivalent mass ofsubstantially pure carbon. Moreover, burning carbon generates about 7500Y calories per kilogram as compared with 3500 to 500 calories perkilogram generated by our modified wood substance. The latter produces alighter, more porous brick than the former because the heatgenerated bycarbon is greatly in excess of the amount required for, fusing thesiliceous material; thus, if the wood product is. too completelyoarbonized, the burning stage of the process will tend to make a denseproduct.

While we prefer to use wood as a base for preparing the modifiedsubstance, any cellular or fibrous combustible substance may be usedinstead of wood. For example, good results may be obtained by usin peat,

partially volatilized and having sub stantially the same chemical andphysical attributes of the modified wood substance.

An improvement onour process as above described consists in adding tothe mixture of clay and woody or other fibrous substance, a light poroussiliceous substance such as kieselguhr or fullers earth, etc.-, of

colloidal siliceous substances such as colloidal wood, and water tobecome product by acting as a sintering agentjor the walls of the poresformed upon combustion of the woody substance. At'thesame time, thefight siliceouslsubstan'ce either enhances, or at least does not.militate against, the We claim:

1. In the ceous objects a cellular or recess of making porous siligmixing a siliceous base with brous substance, making the mixture plasticby adding water forming.

the mixture into shapes, and then drying and burning the shapes; thestep which consists in partially volatiliz'ing the fibrous substancebefore the ormed. v j 2. In the process set forth in claim 1, the stepwhich consists heating the cellular orfibrous substance "until its colorbe;

comes dark brown. i 3. In the process set-forth in shapes are claim, 1,the

porosity of the finished brick. 11

cellular or step which consists in heating the cellular or fibroussubstance until its resiliency or elasticity has been substantiallydestroyed.

4. In the process set forth in claim 1, the step which consists inheating the cellular or fibrous substance under conditions oftemperature and duration of heating which will drive off substantiallyall ingredients which are more volatile' than the acetones but withoutvolatilizing a substantial amount of acetones or ingredients lessvolatile than acetones. I

5. The process of making porous siliceous objects which consists inheating a quantity of wood or other cellular or fibrous substance forabout 10 minutes at a temperature approximately 325 centigrade, mixingabout 125 parts by weight of the resulting modified cellular or fibroussubstance with adding Water to the,

about 100 parts of clay, mixture to render it plastic, forming themixture into shapes, and drying and burning the shapes.

6. In the process set forth in claim 1, the step which consists inadding to the mixture reactive agents which will render the IIllXH tureplastic or act as a flux.

7. In the process set forth in claim 1, the step which consists inadding to the mixture a light porous siliceous substance or colloidalsiliceous substance.

y In testimony whereof the fication is signed.

FERNANDO C. KERN. FREDERICK E. KERN.

foregoing speci-

